1. Field of the Invention
This invention relates to a speed control device of a toric type infinitely variable transmission in which the opposed surfaces of an input disc and an output disc provided on an input shaft and an output shaft, respectively, disposed on the same axis cooperate with each other to form a toroidal cavity and traction rollers are disposed in the toroidal cavity and engaged with the input and output discs and a large torque is transmitted by a traction force produced in the engaged portion, and intends to provide a speed control device which is capable of effecting control of the transmission ratio of acceleration and/or deceleration by a small operating force and which is simple in structure and excellent in durability and moreover inexpensive.
2. Description of the Prior Art
The toric type infinitely variable transmission as described above is known and various speed control device thereof have heretofore been devised. For example, in the toric type infinitely variable transmissions disclosed in U.S. Pat. Nos. 3,087,348; 3,142,189; 3,159,042; 4,086,820; and 4,275,610, a hydraulic cylinder device is provided for each of the traction rollers and the traction rollers are moved by a small amount in the direction of the pivot axis thereof, and in the toric type infinitely variable transmissions disclosed in U.S. Pat. Nos. 3,008,337 and 3,570,317, the pivot shafts of the traction rollers are tilted by a hydraulic cylinder, and in all of these transmissions, self speed controlling action is performed to effect transmission ratio change. Also, as a toric type infinitely variable transmission using no hydraulic device, there is one disclosed in U.S. Pat. No. 2,086,491. This transmission uses not oil pressure but a screw device or a gear device to directly rotate a trunnion about the pivot shaft thereof and does not perform the self speed changing action and therefore requires a large transmission ratio change operating force.
Generally, in the toric type infinitely variable transmission, it is known that when the axis of rotation of traction rollers and the axis of rotation of input and output discs are not aligned with each other, that is, when the trunnion devices which rotatably support the traction rollers are moved by a small amount in the direction of the pivot axis thereof and/or when the pivot shaft is tilted, rotation of the traction rollers about the pivot axis thereof results from the self transmission ratio changing action and the radii of the engaging circles of the traction rollers and the input and output discs are varied, that is, the transmission ratio is varied.